As users demand for more and more network resources, Long Term Evolution Advanced (LTE-Advanced) has proposed the carrier aggregation (CA) technology to deal with the lack of network bandwidth. The idea of carrier aggregation is mainly to integrate the bandwidths of several separated bands, so the data transmission can be more efficient, and the communication speed in the network can be improved.
In prior art, to derive signals in a desired band, the carrier aggregation circuit would adopt a filter having the corresponding band to derive the corresponding signals. In addition, since the impedances on the paths of different filters are different, the carrier aggregation circuit can amplify signals of different bands with different amplifiers for avoiding the loading effects on a transmission path from interfering with the transmissions on other transmission paths. Consequently, the design and the use of carrier aggregation circuit would be rather limited. For example, if the communications device needs to support carrier aggregation for different bands, then the previous carrier aggregation circuit has to be replaced, and a new carrier aggregation circuit would be designed according to the new requirement. Furthermore, since the opened communication bands are different in different countries, it becomes inevitable to face the challenges on designing and manufacturing the carrier aggregation circuits.